Step 1

Assemble the jar: Cut out a round of parchment or wax paper that's the same diameter as the opening of the jar.

Step 2

Place the cheese powder in a 2-quart wide-mouth Mason jar, and tilt the jar as needed to create an even layer at the bottom. Top the cheese with the parchment or wax paper round. Pour in the shells. Seal the jar, and tie with ribbon and a tag containing the cooking instructions.

Step 3

Cook the mac and cheese: Bring a large pot of salted water to a boil. Add the pasta and stir to avoid the pasta from clumping together or sticking to the sides of the pot. Cook until the shells are al dente and not quite fully tender, about 5 minutes. Meanwhile, whisk the cheese powder, milk, and salt together in a large measuring cup or bowl; set aside

Step 4

Drain the water from the pasta. Return the pasta to the pot and place over low heat. Add the butter and stir until melted and the shells are evenly coated. Add the cheese and milk mixture and stir continuously until the pasta is well coated and the sauce thickens but is not totally absorbed, 3 to 5 minutes. Serve immediately.